1. Field of the Invention
This invention relates to a bayonet device for a photographic camera lens barrel, and particularly to a bayonet device having a simple shape and structure, thereby not only reducing the machining thereof, but also attaining substantial improvement in precision and strength.
2. Description of the Prior Art
A camera bayonet device for mounting and dismounting interchangeable lenses on and off the camera must have sufficient coupling precision and strength to enable tight mounting of the lenses, thus ensuring that signal members required for transmitting exposure control signals to the camera side and to the lens side, and interlocking members required for information transmission are maintained at their predetermined positions on the lens side. Further, regarding the structural arrangement on the lens side, a bayonet device on a lens barrel must be provided with claw parts and cut-away parts for engagement with corresponding bayonet parts on the camera side. Additionally, in order to restrict undesirable shifting movement of the lens system in the direction of the optical axes of the lens and the camera when the lens is mounted on the camera, dimensions must be restricted within close tolerances. These requirements result in complex structure and shape for the prior bayonet devices which, in turn, result in an increased number of machining processes. Conventional bayonet devices are made of stainless steel or the like for satisfactory mechanical performance and sufficient strength. Thus, such material is relatively expensive and inferior in workability. Since this material must be machined into a complex shape and structure, it has hardly been possible to lower the material and machining costs. Further, in the conventional bayonet devices, the bayonet member, which is provided on the side of a lens barrel for coupling with the bayonet member on the side of the camera body, not only has a complex shape and structure, but also requires a high degree of machining precision for its coupling face and for its dimensions in the direction of the optical axes of the lens and the camera when the lens is mounted on the camera. Such requirement for precision has also caused an increase in the number of machining processes and hindered cost reduction.
Further, conventional bayonet devices are generally arranged to effect restricted movement in the direction of the optical axes of the lens and the camera by way of resilient forces from a spring provided on the side of the camera and arranged to impose a positional restriction in the direction of its thrust. This spring is arranged in its thrust direction to absorb a tilt of the lens relative to a given angle between its optical axis and a film surface to be exposed, or between its optical axis and a view finder optical system of the camera, and also to absorb shifting or rattling play of the lens when mounted on the camera body. To minimize the tilting and rattling play of the lens, the force of the spring in the thrust direction must be as great as possible. However, a strong force of the spring impedes the lens mounting operation.
Free play is also known to exist in the radial direction of the lens and the camera within a tolerance range of coupling precision. It is desirable to have a certain degree of such play for easing the lens mounting operation. However, such a play, together with the weight of the lens barrel, causes the optical axis of the lens to deviate from the centr of the lens mounting position, and this, in turn, causes the exposure control signal members of the lens and the camera to deviate from their engaging positions. This deviation then makes correct transmission and receipt of signals between the lens and the camera body very difficult.